Many industrial processes involve a mixture of a number of different fluids having different properties, for example, density or concentration. In some cases, knowing the concentration of the components of the mixture is useful for controlling the process. For example, the synthesis of isooctane (i.e., octane) for blending in a dynamic gasoline pool is a step in petroleum refining. One process for producing octane is HF Alkylation. In this process, Hydrogen Fluoride (HF, hydrofluoric acid) serves as a catalyst for the reaction of isobutane and C4 olefins to form octane or “alkylate.” A catalyst is a substance that increases a rate of a chemical reaction without being consumed in the process. The alkylation process turns low-molecular weight hydrocarbons, which formerly were waste, into a component of gasoline.
HF catalyst includes three components—HF (approximately 90%), water (approximately 1%), and acid-soluble organics (ASO) as the remainder. The concentration of each of the components affects the alkylation process. For example, a small concentration of water improves reaction efficiency, whereas a large concentration increases corrosiveness of the catalyst. Further, the concentration of HF can affect its role as a catalyst. For example, in acid runaway, HF's role as a catalyst is compromised when the HF concentration falls below a threshold concentration and begins to participate as a reactant in side reactions that consume HF, but do not produce octane.
Acid runaway can be avoided by knowing HF and ASO concentrations. In particular, to avoid acid runaway, an HF concentration margin can be maintained over the critical concentration. Uncertainty around the HF and ASO concentrations can necessitate a greater margin over the critical concentration and cause a decrease in efficiency. In general, to optimize the alkylation process, the concentrations of the components of the HF catalyst are controlled. Minimizing a net consumption of HF by fine-tuning the operation of the alkylation unit can increase safety and profitability of the unit. For example, large output of octane barrels can be obtained at minimum cost by operating the unit at the lowest possible HF concentration without risking acid runaway. Grab-sampling extraction for laboratory analysis and online analysis are two methods for monitoring the concentrations of the components of HF catalyst (henceforth referred to as “HF mix”).